Electromagnetic Effects in Capacitively Coupled Plasmas

TL;DR

This paper investigates electromagnetic effects in large-area, high-frequency capacitively coupled plasmas, highlighting mode excitation issues that affect plasma uniformity and discussing techniques to mitigate these effects.

Contribution

It identifies when electrostatic models fail and electromagnetic effects become significant in CCPs, providing insights into mode influence and mitigation strategies.

Findings

Electromagnetic modes can disrupt plasma uniformity in large-area CCPs.

Electrostatic approximation breaks down at high frequencies and large electrode sizes.

Techniques to prevent mode excitation improve plasma uniformity.

Abstract

Following requirements of the plasma processing industry for increasing throughput, capacitively coupled plasma reactors with large area electrodes driving by very high frequency sources have been proposed. However, such reactors with plasmas inside support modes which can negatively influence the uniformity in the ion fluxes or the average energy of the ions impinging on the substrates, which is an essential requirement of the industry. It is shown when the popular electrostatic approximation used for description of the fields in capacitively coupled plasmas (CCP) breaks down and when these modes must be treated electromagnetically. Influence of the modes on the essential parameters of the CCP discharges is discussed. A few techniques for avoiding excitation of the modes leading to the undesired nonuniformities are mentioned. Results of several experiments studying such plasma discharges are briefly reviewed.